Optimized interferometrically modulated array source

Abstract

An improved interferometric modulator permits the reduction in size of optical transmitters. In one embodiment, the optical modulator includes amplifiers or attentuators as phase modulators. In another embodiment, two outputs from a combiner are fed to the modulator, thus avoiding the requirement for an input splitter in the modulator. Light passing through the modulator may be both phase-shifted and amplified or attenuated by optical regulator sections located in the modulator. In another embodiment, the transmitter is included as a multiple-wavelength optical communications source, where individual current sources are provided to actuate a number of light sources feeding into the combiner, a processor controls the operation of each light source, and a modulator driver receives a data input signal to be encoded on the output of the source. By combining a number of modulators, a gray scale modulator may be fabricated for producing a gray scale output, rather than a conventional binary level output.

We claim: 
     
       1. An optical transmitter, comprising: a substrate;   a plurality of selectively actuatable light sources disposed on the substrate;   a first optical combiner region disposed on the substrate, light from each of the light sources being input to the combiner region;   two output ports outputting light from the combiner region; and   a first interferometric modulator disposed on the substrate and having a first and second light path to receive light from the first optical combiner region, the first light path being optically coupled at one end to one of the two output ports and the second light path being optically coupled at one end to the other of the two output ports, other ends of the light paths being combined into a single output.   
     
     
       2. An optical transmitter as recited in claim 1, wherein the first optical combiner region comprises a star coupler. 
     
     
       3. An optical transmitter as recited in claim 1, wherein the first interferometric modulator comprises a Mach-Zehnder modulator. 
     
     
       4. An optical transmitter as recited in claim 1, wherein the first interferometric modulator comprises first and second phase modulators disposed in the first and second light paths respectively. 
     
     
       5. An optical transmitter as recited in claim 1, wherein the first interferometric modulator comprises first and second optical power regulators disposed in the first and second light paths respectively. 
     
     
       6. An optical transmitter as recited in claim 1, wherein the selectively actuatable light sources are single longitudinal mode lasers, each having a unique corresponding output frequency. 
     
     
       7. An optical transmitter as recited in claim 1, further comprising a second interferometric modulator disposed on the substrate and optically coupled to third and fourth outputs from the first combiner, and a second optical combiner region disposed on the substrate and optically coupled to outputs from the first and second interferometric modulators. 
     
     
       8. An optical transmitter system, for transmitting an optical signal using a data input signal, comprising: a multiplexed optical source, including   a substrate,   a plurality of selectively actuatable light sources disposed on the substrate,   an optical combiner region disposed on the substrate, each of the light sources being optically coupled as respective inputs to the combiner region   two output ports outputting light from the combiner region, and   an interferometric modulator disposed on the substrate and having a first and second light path to receive light from the first optical combiner region, the first light path being optically coupled at one end to one of the two output ports and the second light path being optically coupled at one end to the other of the two output ports, other ends of the light paths being combined into a single output;   a plurality of individually actuatable current sources, each connected to a respective light source;   a processor coupled to control the plurality of individually actuatable current sources; and   an input/output driver provided to drive the interferometric modulator in response to the data input signal.   
     
     
       9. A system as recited in claim 8, wherein the input/output driver comprises an input data port provided to receive parallel electrical input signals, a multiplexer coupled to the input data port to multiplex the parallel electrical signals and produce a multiplexed electrical output signal, and a modulator driver coupled to the multiplexer and the interferometric modulator, to receive the multiplexed electrical output signal and transmit a modulator drive signal to the interferometric modulator in response to the multiplexed electrical output signal. 
     
     
       10. A system as recited in claim 8, wherein the input/output driver comprises a detector provided to detect an optical input signal, an amplifier coupled to the detector to generate an amplified signal in response to the detected optical input signal, and a modulator driver coupled to the amplifier and the interferometric modulator, to receive the amplified signal and to transmit a modulator drive signal to the interferometric modulator in response to the amplified signal. 
     
     
       11. A system as recited in claim 8, further comprising a thermal control unit coupled to the multiplexed optical source and the processor to maintain a temperature of the multiplexed optical source within a predetermined range. 
     
     
       12. A system as recited in claim 8, wherein the plurality of selectively actuatable light sources comprise a plurality of lasers, each having a unique corresponding frequency. 
     
     
       13. A system as recited in claim 8, wherein the optical combiner region comprises a star coupler. 
     
     
       14. A system as recited in claim 8, wherein the interferometric modulator comprises a Mach-Zehnder modulator. 
     
     
       15. A system as recited in claim 14, wherein the interferometric modulator comprises first and second amplifiers in the first and second light paths respectively. 
     
     
       16. A system as recited in claim 15, further comprising a controller to control amplification by the first and second amplifiers so as to optimize depth of modulation of light modulated by the interferometric modulator. 
     
     
       17. A system as recited in claim 14, wherein the interferometric modulator comprises first and second phase modulators in the first and second light paths respectively. 
     
     
       18. An optical transmitter system, for transmitting an optical signal using a data input signal, comprising: a multiplexed optical source, including a substrate,   a plurality of selectively actuatable light sources disposed on the substrate,   an optical combiner region disposed on the substrate, each of the light sources being coupled as respective inputs to the optical combiner region, and   an interferometric modulator disposed on the substrate and coupled to an output from the optical combiner region, the modulator including an optical regulator in at least one modulator arm;     a plurality of individually actuatable current sources, each connected to a respective light source;   a processor coupled to control the plurality of individually actuatable current sources; and   an input/output driver provided to drive the interferometric modulator in response to the data input signal.   
     
     
       19. A system as recited in claim 18, wherein the optical regulator comprises an optical amplifier. 
     
     
       20. A system as recited in claim 18, wherein the optical regulator comprises an optical attenuator.